Will STAT-C Replace Today's HCV Standard Therapy?
A new era of medical technology is currently emerging for Hepatitis C treatment. The development of specifically targeted antiviral therapy for Hepatitis C (STAT-C) is rapidly advancing and will revolutionize the way this virus is treated.
Today’s standard treatments are based on interferon, a medication that works by modifying the immune system response. However, by targeting the Hepatitis C virus, STAT-C uses a more direct approach than interferon-based therapies.
Although several therapeutic regimens have been developed to treat Hepatitis C, they all focus on interferon. The current standard of care for the treatment of Hepatitis C is combination therapy with pegylated interferon-alfa and ribavirin. While this combination regimen boasts an 80 percent success rate for those infected with Hepatitis C genotype 2, only about 40 percent undertaking this therapy achieve success with genotype 1, the most common Hepatitis C subtype in North America. Hepatitis C treatment programs centered on interferon are limited by three primary factors:
- Side Effects – Enduring interferon treatment is a challenge; approximately 50 percent of patients are forced to reduce the dosage or stop treatment prematurely due to the severity of side effects.
- Efficacy – Interferon’s effectiveness is limited; of those who are able to complete treatment at full dosage, approximately only 50 percent achieve sustained virologic response (SVR), otherwise known as an undetectable viral load.
- Duration – The amount of time in treatment is long; duration times typically range from six months to one year.
Concerns about the efficacy and tolerability of standard peginterferon/ribavirin therapy suggest there is a significant medical need for improved therapies for Hepatitis C. As supported thus far by clinical trial results, the hope for STAT-C is to improve on the three factors limiting interferon treatment: improvement in viral elimination, higher patient tolerability and shorter treatment duration.
Instead of stimulating the body’s natural immune response to the virus, STAT-C directly attacks the Hepatitis C virus. Similar to some of the drugs used to treat HIV, these new medications thwart the enzymes needed for the virus to reproduce.
Drug resistance is one of the larger obstacles STAT-C must contend with. Similar to HIV therapy, the antiviral agents composing STAT-C possibilities are limited by being prone to drug resistance. When the virus alters itself to avoid extinction, drug resistance renders the drug useless and makes the new strain even harder to eliminate. However, researchers have found that Hepatitis C resistance may be delayed or prevented by using combinations of potent antiviral drugs without cross-resistance profiles and optimizing patient adherence to therapy.
In terms of possible new anti-virals in the pipeline, the medications thus far are targeting two enzymes required for Hepatitis C reproduction: serine protease and polymerase. Known as Hepatitis C protease and polymerase inhibitors, the early clinical data on this class of drugs is encouraging despite issues of toxicity and virus resistance. Inhibiting these two enzymes has emerged as preferred contenders in the realization of STAT-C.
- Protease Inhibitors – Examples of protease inhibitors currently being developed and tested include SCH503034, VX-950 (Telaprevir), VX500, R7227, ITMN-191, ACH-1095 and TMC435350. While a few of these have been abandoned or altered due to their potential toxicity, the clinical promise of protease inhibitors is enormous. Especially when combined with pegylated interferon alfa-2a and ribavirin, most studies recruiting this triple combination demonstrate superiority in rapid Hepatitis C viral load decline.
- Polymerase Inhibitors – Examples of polymerase inhibitors currently being developed and tested include GS9190, GSK625433, R7128, R1626, VCH-759, MK-0608, IDX-184, A-837093, and AG-021541. While some reports on these agents to date have revealed drug resistance and gastrointestinal side effects, the bottom line is polymerase inhibitors have the potential to dramatically drop viral load in a short period of time. As their evaluation continues, an increasing number of researchers are combining polymerase inhibitors with pegylated interferon alfa-2a for greater efficacy.
It is important to remember that many investigational agents never make it out of the development pipeline, either due to suboptimal efficacy or poor safety. However, incorporating the approaches of enzyme inhibition with immune therapy may provide a cure for a substantial percentage of people with Hepatitis C. Experts in the field agree that STAT-C drugs combined with pegylated interferon and possibly ribavirin are the future for treating Hepatitis C.
We can expect that therapy for Hepatitis C will become more complicated, similar to highly active antiretroviral therapy (HAART) used to fight HIV infection. Also like HAART, physicians and researchers must be cautious working with STAT-C, as the virus may become more sophisticated and resist the medications used. Although STAT-C is not a single-pill cure-all, its ability to reduce viral load in a relatively short period of time will revolutionize how Hepatitis C is treated.
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www.hcvadvocate.org, Hepatitis C Treatments in Current Clinical Development, Alan Franciscus, January 2008.
www.medscape.com, Specifically Targeted Antiviral Therapy (STAT-C) for Patients With Chronic Hepatitis C, Zobair M. Younossi, MD, MPH, FACP, FACG, Medscape, 2007.
www.projectsinknowledge.com, Revolutionizing the Way We Treat HCV: Stat-C, Ira M. Jacobson, MD, John G. McHutchison, MD, FRACP, Jean-Michel Pawlotsky, MD, PhD, Charles M. Rice, PhD, Projects In Knowledge, Inc., 2007.